Expand / Collapse all hierarchy in Outliner
Simply click on expand arrow with Shift key.
It will expand/collapse everything under it. So if you need ...


expand all (under collection) - click on Collection
expand only specific bone chain - click on Armature


Example with and without Shift key:



Or use "+" / "-" key (with cursor in Outliner Editor) to open / close one level. 

More details in Blender Manual.